Stroke, a sudden development of a focal neurologic deficit, remains as a frequent leading cause of death even in Korea. Five to 13% of strokes occur in patients with younger than 45 years of age; up to 40% of strokes occur in patients without occlusive cerebrovascular disease; and it is estimated that the source is cardiac origin in 15 to 20%. Another 30n to 40% are in the category of stroke of undetermined cause, also known as cryptogenic stroke. An increasing number of echocardiographic findings have been found in this group of cryptogenic stroke patients and in patients with embolic stroke. Cardiac tumors can be a source of emboli, but the most commonly implicated sources are thrombi from the left atrial appeadage or left ventricle, left atrial spontaneous contrast, atrial septal aneurysm associated with a patent foramen ovale (PFO), thrombi traversing a PFO, valve vegetations, protruding aortic atheroma of aortic arch, and emboli associated with mitral and aortic prostheses. Echocardiography is most helpful in defining the cause of cerebrovascular ischemia in patients without occlusive cerebrovascular disease. For complete evaluation of potential source of cardiac embolic sources, transesophageal echocardiography (TEE) is required because many of the entities such as left atrial appendage thrombus can be detected only with this technique.